Introduction.

Workshop PG5
Project management
6.2 Cyclic Blocks (COB 0 ... 15)
The fact that your SB is waiting on an event must under no circumstances block the
rest of the program from being executed continuously. To prevent you from programming
such a structure, a SB must be called from a COB. You can’t have a SB
without a COB!
The SB then will be called once a cycle and the state will be tested. If the SB is
waiting on an event, then the program simply returns to the COB and continues to
execute the COB. The next step of the SB will not be executed until the next cycle
in which it is not in a waiting state.
Cycle starts
here
Cyclic
programs:
Cycle time:
Cycle
ends here
Until now our programs have been executed in an endless loop. They always started
at the beginning of a COB and then one COB after the other was executed until the
program reached the last COB. Once the program reaches the end, it automatically
returns to the beginning of the first COB and starts the cycle all over again.
The time it takes to execute all the COB’s from the beginning of the first COB to the
end of the last COB, depends on the number and type of instructions and FBOX’s
you use in your program. This time is called Cycle time.
The cycle time is typically in the millisecond range. If you know the cycle time, then
you know how long it takes for a PCD output to react on the change of the state of
an input.
Cyclic programs are built with program blocks like COB’s, PB’s, FB’s, SB’s or
XOB’s.
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